The present invention relates to an auxiliary hydraulic drive for a trailer tractor combination, which combination may include a driven vehicle and a trailer articulately connected thereto or a tractor having a saddle to which the trailer is pivotally connected.
It is already known to provide on the trailing vehicle an auxiliary hydraulic drive to thereby increase the drive adhearance of the trailing vehicle during travel of the tractor-trailer combination over every terrain even if wet, slippery, icy or covered with snow. This arrangement consists essentially in providing at least one axle of the trailer with an auxiliary hydraulic motor which can be actuated at any time chosen by the driver. Such auxiliary hydraulic motor is driven by hydraulic fluid supplied by a pump driven by the drive motor of the tractor.
An improvement of the aforementioned arrangement consists to provide the hydraulic circuit with a self-regulating pressure system to avoid deterioration of the hydraulic motor due to variations of the torque applied to the wheels driven by the hydraulic motor which will result from a difference of the adherence of the wheels to the ground over which the vehicle is passing. However, despite this known regulator system it has been necessary to uncouple the wheels from the hydraulic motor whenever the speed of movement of the tractor-trailer combination surpasses about 15 kilometers per hour, and it has been also necessary to stop the tractor-trailer combination in order to recouple the hydraulic motor to the wheels. This inconvenience is especially pronounced if the tractor-trailer combination has to move through long distances over different terrain since this may entail the risk of total immobilization in the event the driver carries out wrong operations.